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The Java collections framework supports generics to specify the type of objects stored in a collection instance. In 1998, Gilad Bracha, Martin Odersky, David Stoutamire and Philip Wadler created Generic Java, an extension to the Java language to support generic types. [4] Generic Java was incorporated in Java with the addition of wildcards.
The Collection interface is a subinterface of java.lang.Iterable, so any Collection may be the target of a for-each statement. (The Iterable interface provides the iterator() method used by for-each statements.) All Collections have an java.util.Iterator that goes through all of the elements in the Collection. Collection is generic.
Boxing's most prominent use is in Java where there is a distinction between reference and value types for reasons such as runtime efficiency and syntax and semantic issues. In Java, a LinkedList can only store values of type Object. One might desire to have a LinkedList of int, but this is not directly possible.
In computer programming, a collection is an abstract data type that is a grouping of items that can be used in a polymorphic way. Often, the items are of the same data type such as int or string . Sometimes the items derive from a common type; even deriving from the most general type of a programming language such as object or variant .
Collections of data objects are typically stored in Java collection classes, such as implementations of the Set and List interfaces. Java generics, introduced in Java 5, are also supported. Hibernate can be configured to lazy load associated collections. [2]: 289–293 Lazy loading is the default as of Hibernate 3.
In Java, is-a relation between the type parameters of one class or interface and the type parameters of another are determined by the extends and implements clauses. Using the Collections classes, ArrayList<E> implements List<E>, and List<E> extends Collection<E>. So ArrayList<String> is a subtype of List<String>, which is a subtype of ...
When applied to a field, the Java volatile keyword guarantees that: (In all versions of Java) There is a global ordering on the reads and writes to a volatile variable. This implies that every thread accessing a volatile field will read its current value before continuing, instead of (potentially) using a cached value. (However, there is no ...
When primitive and value types are used as generic arguments, they get specialized implementations, allowing for efficient generic collections and methods. As in C++ and Java, nested generic types such as Dictionary<string, List<int>> are valid types, however are advised against for member signatures in code analysis design rules. [29]